1. Field of the Invention
The present invention relates to voltage controlled oscillators.
2. Description of the Related Art
A voltage controlled oscillator (VCO) is generally controlled by a voltage input to modify the oscillation frequency of a generated oscillation signal.
In conventional VCO circuits, the voltage input has to be great enough to trigger oscillation. FIG. 1 shows a relationship between a voltage input VCNT and an oscillation frequency fout of a conventional VCO circuit. As shown, when the voltage input VCNT is within a silent region 102, the VCO is silent and the oscillation frequency fout is zero.